mirror of
https://github.com/hsoft/collapseos.git
synced 2024-11-06 01:30:55 +11:00
84 lines
3.4 KiB
Markdown
84 lines
3.4 KiB
Markdown
# Writing to a AT28 from Collapse OS
|
|
|
|
## Goal
|
|
|
|
Write in an AT28 EEPROM from within Collapse OS so that you can have it update
|
|
itself.
|
|
|
|
## Gathering parts
|
|
|
|
* A RC2014 Classic that could install the base recipe
|
|
* An extra AT28C64B
|
|
* 1x 40106 inverter gates
|
|
* Proto board, RC2014 header pins, wires, IC sockets, etc.
|
|
|
|
## Building the EEPROM holder
|
|
|
|
The AT28 is SRAM compatible so you could use a RAM module for it. However,
|
|
there is only one RAM module with the Classic version of the RC2014 and we
|
|
need it to run Collapse OS.
|
|
|
|
You could probably use the 64K RAM module for this purpose, but I don't have one
|
|
and I haven't tried it. For this recipe, I built my own module which is the same
|
|
as the regular ROM module but with `WR` wired and geared for address range
|
|
`0x2000-0x3fff`.
|
|
|
|
If you're tempted by the idea of hacking your existing RC2014 ROM module by
|
|
wiring `WR` and write directly to the range `0x0000-0x1fff` while running it,
|
|
be aware that it's not that easy. I was also tempted by this idea, tried it,
|
|
but on bootup, it seems that some random `WR` triggers happen and it corrupts
|
|
the EEPROM contents. Theoretically, we could go around that by putting the AT28
|
|
in write protection mode, but I preferred building my own module.
|
|
|
|
I don't think you need a schematic. It's really simple.
|
|
|
|
## Building the kernel
|
|
|
|
For this recipe to work, we need a block device for the `at28w` program to read
|
|
from. The easiest way to go around would be to use a SD card, but maybe you
|
|
haven't built a SPI relay yet and it's quite a challenge to do so.
|
|
|
|
Therefore, for this recipe, we'll have `at28w` read from a memory map and we'll
|
|
upload contents to write to memory through our serial link.
|
|
|
|
`at28w` is designed to be ran as a "user application", but in this case, because
|
|
we run from a kernel without a filesystem and that `pgm` can't run without it,
|
|
we'll integrate `at28w` directly in our kernel and expose it as an extra shell
|
|
command (renaming it to `a28w` to fit the 4 chars limit).
|
|
|
|
For all this to work, you'll need [glue code that looks like this](glue.asm).
|
|
Running `make` in this directory will produce a `os.bin` with that glue code
|
|
that you can install in the same way you did with the basic RC2014 recipe.
|
|
|
|
If your range is different than `0x2000-0x3fff`, you'll have to modify
|
|
`AT28W_MEMSTART` before you build.
|
|
|
|
## Writing contents to the AT28
|
|
|
|
The memory map is configured to start at `0xd000`. The first step is to upload
|
|
contents at that address as documented in ["Load code in RAM and run it"][load].
|
|
|
|
You have to know the size of the contents you've loaded because you'll pass it
|
|
as at argument to `a28w`. You can run:
|
|
|
|
Collapse OS
|
|
> bsel 0
|
|
> seek 00 0000
|
|
> a28w <size-of-contents>
|
|
|
|
It takes a little while to write. About 1 second per 0x100 bytes (soon, I'll
|
|
implement page writing which should make it much faster).
|
|
|
|
If the program doesn't report an error, you're all good! The program takes care
|
|
of verifying each byte, so everything should be in place. You can verify
|
|
yourself by `peek`-ing around the `0x2000-0x3fff` range.
|
|
|
|
Note that to write a single byte to the AT28 eeprom, you don't need a special
|
|
program. You can, while you're in the `0x2000-0x3fff` range, run `poke 1` and
|
|
send an arbitrary char. It will work. The problem is with writing multiple
|
|
bytes: you have to wait until the eeprom is finished writing before writing to
|
|
a new address, something a regular `poke` doesn't do but `at28w` does.
|
|
|
|
[load]: ../../../doc/load-run-code.md
|
|
|